A known torque fluctuation absorber is provided, for example, on a drivetrain between an engine and a transmission. The known torque fluctuation absorber absorbs (restrains) torque fluctuations between the engine and the transmission. The known torque fluctuation absorber includes, for example, a damper portion that absorbs (restrains) the torque fluctuations by means of a spring force, a hysteresis portion that absorbs (restrains) the torque fluctuations by means of a hysteresis torque generated by friction, and a limiter portion that generates slippage when torsion generated between a rotational shaft of the engine and a rotational shaft (an input shaft) of the transmission may not be restrained by the damper portion and the hysteresis portion.
In the limiter portion of the known torque fluctuation absorber disclosed, for example, in JP2005-127507A (which will be hereinafter referred to as Reference 1), friction members fixed to both surfaces of a disc are sandwiched between first and second frictional surface plates. The second frictional surface plate is configured so as not to rotate relative to the first frictional surface plate and so as to move in an axial direction of the input shaft of the transmission. The second frictional surface plate is biased by a disc spring toward the friction members. The disc spring in the limiter portion has a continuous annular shape. An outer circumferential end of the disc spring is supported by a holding plate while an inner circumferential end of the disc spring is in contact with the second frictional surface plate. Thus, the disc spring is assembled on the known torque fluctuation absorber while being inclined from the outer circumferential end to the inner circumferential end.
In addition, in a thrust portion (corresponding to the hysteresis portion) of the known torque fluctuation absorber disclosed in Reference 1, a flange portion of the hub is arranged between first and second side plates fixed to the disc. A first thrust member is arranged between the first side plate and the flange portion. A disc spring and a second thrust member are arranged between the second side plate and the flange portion. The second thrust member is biased by the disc spring. The disc spring in the hysteresis portion has a continuous annular shape. An outer circumferential end of the disc spring is supported by the second side plate while an inner circumferential end of the disc spring is in contact with the second thrust member. Thus, the disc spring is assembled on the known torque fluctuation absorber while being inclined from the outer circumferential end to the inner circumferential end.
Here, lifetimes of the limiter portion and the hysteresis portion may not depend on a thickness of each of the friction members but on a wear allowance of the friction member (i.e., the lifetimes of the limiter portion and the hysteresis portion are determined by a range where the disc spring may apply a load equal to or greater than a load required for biasing the friction member). The wear allowance is determined by a load of the disc spring. According to the known torque fluctuation absorber disclosed in Reference 1, the wear allowance of the friction member may not be increased due to the configuration of each of the limiter portion and the hysteresis portion. According to the configuration of each of the limiter portion and the hysteresis portion in Reference 1, the disc spring is sandwiched between two members. In addition, for example, when the disc spring is assembled on the known torque fluctuation absorber while being not inclined from the outer circumferential end to the inner circumferential end (i.e. in a state where the inner circumferential end is linear to the outer circumferential end in a direction perpendicular to the axial direction) or when the disc spring is assembled on the known torque fluctuation absorber substantially in the aforementioned condition, the spring may be brought into a firm contact with the two members. Therefore, the disc spring is consistently utilized only in a position obtained before the disc spring is flexibly deformed and compressed into a linear shape in the direction perpendicular to the axial direction. As a result, the lifetimes of the limiter portion and the hysteresis portion may shorten.
A need thus exists for a torque fluctuation absorber, which is not susceptible to the drawback mentioned above.